.beta.-hemoglobinopathies are a group of inherited disorders of .beta.-globin biosynthesis. Although efforts have concentrated on a variety of therapeutic regimens, feasible clinical treatments for these debilitating diseases remain scarce.
Various therapies have been utilized in the treatment of .beta.-hemoglobinopathies, each accompanied by drawbacks. G. P. Rogers et. al., "Current and Future Strategies for the Management of Hemoglobinopathies and Thalassemia", Hematology 1994, Education Program American Society of Hematology, pp. 9-20 (1994). Although the chemotherapeutic agent hydroxyurea stimulates fetal hemoglobin production and reduces sickling crisis in sickle cell anemia patients, its use in monotherapy is potentially limited by myelotoxicity and the risk of carcinogenesis. Potential long term carcinogenicity is also a drawback of 5-azacytidine-based therapies. Red blood cell transfusions expose patients to the potential of a wide range of infectious viral agents, as well as alloimmunization. Bone marrow transplants are not a readily available option for a large number of patients. Erythropoietin-based therapies have not proved consistent among a range of patient populations. Such varying drawbacks contraindicate the long term use of such agents or therapies.
It is clear from multicenter studies involving numerous patients with sickle cell disease that increased blood levels of fetal hemoglobin are associated with lower events of sickle cell crisis and longer survival time O. S. Platt et al., "Pain in Sickle Cell Disease, New Eng. J. Med., 325, pp. 11-16 (1991); O. S. Platt et al., "Mortality ion Sickle Cell Disease", New Eng. J. Med., 330, pp. 1639-44 (1994)!. Accordingly, in an effort to avoid the disadvantages of conventional therapies for .beta.-hemoglobinopathies, therapies have centered around ways to increase fetal hemoglobin production. Recent clinical trials have used butyrate analogs, including arginine butyrate and isobutyramide, to stimulate fetal hemoglobin production as a means of treatment S. Perrine et al., A Short Term Trial of Butyrate to Stimulate Fetal-Globin-Gene Expression in the .beta.-globin Disorders", N. Eng. J. Med., 328, pp. 81-86 (1993); S. P. Perrine et. al., "Isobutyramide, an Orally Bioavailable Butyrate Analogue, Simulates Fetal Globin Gene Expression In Vitro and In Vivo", British J. Haematology, 88, pp. 555-61 (1994); A. F. Collins et al., "Oral Sodium Phenylbutyrate Therapy in Homozygous .beta. Thalassemia: A Clinical Trial", Blood, 85, pp. 43-49 (1995).
Following the observation that butyric acid induces cell differentiation in vitro A. Leder and P. Leder, "Butyric Acid, a Potent Inducer of Erythroid Differentiation in Cultured Erythroleukemic Cells", Cell, 5, pp. 319-22 (1975)!, that compound was found to demonstrate promising effects in leukemia patients, by inducing cell differentiation A. Novogrodsky et al., "Effect of Polar Organic Compounds on Leukemic Cells", Cancer, 51, pp. 9-14 (1983)!. Aside from their use in treating .beta.-hemoglobinopathies, butyrate derivatives such as arginine butyrate, an arginine salt of butyric acid, have been shown to exert anti-tumor and anti-leukemia effects in mice C. Chany and I. Cerutti, "Antitumor Effect Of Arginine Butyrate in Conjunction with Corynebacterium Parvum and Interferon", Int. J. Cancer, 30, pp. 489-93 (1982); M. Otaka et al., "Antibody-Mediated Targeting of Differentiation Inducers To Tumor Cells: Inhibition of Colonic Cancer Cell Growth in vitro and in vivo", Biochem. Biophys. Res. Commun., 158, pp. 202-08 (1989); O. Vincent-Fiquet, J. C. Rogez, F. Boitte, M. Brazier and G. Desmet, "Effects of Arginine Butyrate and Tributyrylxylitol on Cultured Human Sarcoma Cells", Anticancer Research, 14, pp. 1823-28 (1994)!.
Sodium butyrate has been found to induce apoptosis in retinoblastoma cell lines Robert M. Conway, Michele C. Madigan, Philip L. Penfold and Francis A. Billson, "Induction of Apoptosis by Sodium Butyrate in the Human Y-79 Retinoblastoma Cell Line", Oncology Research, Vol. 7, No. 6, pp. 289-97 (1995)! and modify antigen expression in pancreatic cancel cells Stefano Corra, Katherine Kazakoff, Masatoshi Mogaki, Martin Cano, and Parviz M. Pour, "Modification of Antigen Expression in Human and Hamster Pancreatic Cancer Cell Lines Induced by Sodium Butyrate", Teratogenesis, Carcinogenesis, and Mutagenesis, 13, pp. 199-215 (1993)!.
The differentiating ability of butyrates is enhanced when administered in conjunction with other active agents. The combination of butyrates with the active metabolite of vitamin D shows enhanced differentiation of human colonic carcinoma cells in vitro Y. Tanaka, K. K. Bush, T. M. Klauck, P. Higgins, "Enhancement of Butyrate Induced Differentiation of HT-29 Human Colon Carcinoma Cells by 1,25-Dihydroxyvitamin D.sub.3 ", Biochem. Pharmacol. 38, pp. 3859 (1989)!. Other agents known to exhibit this synergism with butyrates include all trans-retinoic acid Z. Chen and T. Breitman, "Tributyrin: A Prodrug of Butyric Acid for Potential Clinical Application in Differentiation Therapy",Cancer Res., 54, pp. 3494-99 (1994)!, TNF-.alpha. (Tumor Necrosis Factor)Yifan Zhai et al, Development and Characterization of Recombinant Adenoviruses Encoding MART1 or gp100 for Cancer Therapy, The Journal of Immunolgy, pp. 700-710 (1996)! and dibutyryl adenosine-3', 5'-cyclic monophosphate Paul S. Ebert and Michael Salcman, "Differentiation Therapy Is Potentiated by Chemotherapy and Hyperthermia in Human and Canine Brain Tumor Cells In Vitro", Neurosurgery, Vol. 34, No. 4, pp. 657-663 (1994)!.
Butyrates have also been tested for use in combination therapy in conjunction with a known therapeutic agent. A combination of Interleukin 2 and sodium butyrate has been investigated for treatment of colo-rectal cancer Pacale Perrin et al, An Interleukin 2/Sodium Butyrate Combination as Immunotherapy for Rat Colon Cancer Peritoneal Carcinomatosis, Gastroenterology, 107, pp.1697-1708 (1994)!.
Butyrate salts induce differentiation of colon cancer cell lines and arrest the growth of neoplastic colonocytes O. C. Velazquez, H. M. Lederer, and J. L. Rombeau, "Butyrate and the Colonocyte. Implications for Neoplasia", Dig. Dis. Sci., 41, pp.727-39 (1996)!. Sodium butyrate has been shown to induce apoptosis in colorectal carcinoma cell lines and to inhibit urokinase plasminogen activator and its receptor mRNA expression in colon cancer cell lines A. Hague, D. J. Elder, D. J. Hicks, and C. Paraskeva, "Apoptosis in Colorectal Tumour Cells: Induction by the Short Chain Fatty Acids Butyrate, Propionate And Acetate and by the Bile Salt Deoxycholate", Int. J. Cancer, 60, pp.400-6 (1995); Jinjin Dang, Yao Wang and William F. Doe, "Sodium Butyrate Inhibits Expression Of Urokinase And Its Receptor mRNAs At Both Transcription And Post-transcription Levels In Colon Cancer Cells", FEBS Letts., 359, pp. 147-50 (1995)!. Butyrates, in conjunction with a known therapeutic agent, are known to be effective in the apoptosis of colon cancer cells John A. McBain et al, "Phorbol Ester Augments Butyrate-Induced Apoptosis Of Colon Cancer Cells", Int. J. Cancer, 67, pp. 715-723 (1996)!.
In addition to colon cancer, butyrates have been investigated for the treatment of inflammatory bowel diseases, such as colitis and Crohn's disease. Butyrates enhance the synthesis of colonic mucin, a glycoprotein present in the colonic mucus. The mucus adheres to the colonic epithelium, thereby preventing invasion by colonic bacteria and protecting against damage by bacterial toxins and enzymes. Butyrate enemas are used in the treatment of diversion colitis and ulcerative colitis W. Frankel et al, "Butyrate Increases Colonocyte Protein Synthesis In Ulcerative Colitis", Journal of Surgical Research, 57, pp. 210-214 (1994); A. Finnie et al, "Colonic Mucin Synthesis is Increased by Sodium Butyrate", Gut, 36, pp. 93-99 (1995)!.
Although butyrate salts have the advantage of low toxicity as compared with conventional chemotherapeutic agents, their short half-lives in vivo have been viewed as a potential obstacle in clinical settings A. Miller et al., "Clinical Pharmacology of Sodium Butyrate in Patients with Acute Leukemia", Eur. J. Clin. Oncol., 23, pp. 1283-87 (1987); Novogrodsky et al. supra!. The rapid clearance of these agents results in an inability to deliver and maintain high plasma levels of butyrate which necessitates administration by intravenous infusion. Another potential obstacle to the use of butyrate salts is salt overload and its physiological sequelae.
In view of these observations, various prodrugs of butyric acid have been proposed for use in .beta.-hemoglobinopathy and leukemia differentiation therapies. Such prodrugs include tributyrin and n-butyric acid mono- and polyesters derived from monosaccharides Z. Chen and T. Breitman, "Tributyrin: A Prodrug of Butyric Acid for Potential Clinical Application in Differentiation Therapy", Cancer Res., 54, pp. 3494-99 (1994); H. Newmark et al., "Butyrate as a Differentiating Agent: Pharmacokinetics, Analogues and Current Status", Cancer Letts., 78, pp. 1-5 (1994); P. Pouillart et al., "Pharmacokinetic Studies of N-Butyric Acid Mono- and Polyesters Derived From Monosaccharides", J. Pharm. Sci., 81, pp. 241-44 (1992); C. Calabresse et al, "Selective Induction Of Apoptosis In Myeloid Leukemic Cell Lines By Monoacetone Glucose-3 Butyrate", Biochem. Biophys. Res. Comm., Vol. 201, No. 1, pp. 266-82 (1994)!.
Such butyrate prodrugs have not proved useful as therapeutics, however, due to factors such as short half-life, low bioavailability, low C.sub.max, or lack of effective oral deliverability. Other prodrugs, such as AN-9 and AN-10 A. Nudelman et al., "Novel Anticancer Prodrug of Butyric Acid", J. Med. Chem., 35, pp. 687-94 (1992)!, elicit metabolites that may produce formaldehyde in vivo, leading to toxic effects in patients.
To date, conventional methods and therapeutic agents have not proved to be safe and effective for all patients in the treatment of .beta.-hemoglobinopathies. This is also the case for diseases characterized by neoplastic, tumorigenic or malignant cell growth, or malignant hematological disorders Dennis A. Casciato and Barry B. Lowitz, Manual of Clinical Oncology, Little, Brown and Company, Third Edition, pp. 39-71 (1995); Roland T. Skeel and Neil A. Lachant, Handbook of Cancer Chemotherapy, Little, Brown and Company, Fourth Edition, pp. 123-197 (1995)!. Accordingly, the need exists for alternatives having advantages over, and avoiding the disadvantages of, such conventional methods and agents, while providing effective therapy for those target diseases.